1. Field of the Invention
The present invention relates to a rear suspension for a motor vehicle.
2. Description of the Prior Art
There has been known an automotive rear suspension of the type as disclosed in U.S. Pat. No. 4,269,432 in which the rear suspension includes a wheel support for rotatably supporting the rear wheel, a pair of front and rear lateral links for supporting the wheel support on the vehicle body so that it is swingable in the vertical and longitudinal directions of the vehicle body, and a trailing link for supporting resiliently either one of the wheel support and the connecting portion of the lateral links with the wheel support so that the wheel support is allowed to travel a short distance in the longitudinal direction of the vehicle body. The distance between the outer connecting points of the lateral links with the wheel support is set to be smaller than that between the inner connecting points thereof with the vehicle body. Alternatively, the front lateral link is set to be shorter than the rear lateral link. By these arrangements, when rearward forces such as a braking force act on the rear wheels, the support member for the rear wheel is caused to travel rearward, and the rear wheel changes in position in the direction of the toe-in. Thus, vehicle motional stability is obtained.
Recently, developments have been made in rear suspension systems of the above-mentioned types so that a vehicle body displays desired characteristics according to motional conditions by means of toe-control of the rear wheels relative to lateral forces acting thereon. Such toe-control can be obtained by setting the characteristics of either the front or rear suspension system to be non-linear in repsonse to lateral forces acting on the rear wheel. For example, U.S. Pat. No. 4,621,830 discloses this type of automotive rear suspension which is desirably applied to a front-engine, front-wheel-drive type of motor vehicle which exhibits a tendency toward excessive under-steer when the magnitude of the lateral force is large. The suspension includes a front lateral link system, whose deformation characteristics are set to be non-linear. More specifically, a bush disposed between the lateral link and the vehicle body is set to exhibit a non-linear deformation characteristic. When the lateral force acting on the rear wheel becomes extremely large, such as during a sudden turn or changing of lanes at high speed, the rear wheel is controlled in its attitude so as to decrease the change in the toe-out direction, that is, to weaken the understeer characteristics so that drivability is improved, while driving stability is ensured with the application of a small magnitude of lateral force, or when the vehicle is moving at medium or low speed.
In a suspension system as described above, when the rear wheels are subjected to rearward force, the wheel supports for the rear wheels are caused to travel in the rearward direction to produce a toe-in movement therein. At the same time, there are produced deformations caused by the elastic deformation of the bushes etc. in the front and rear lateral link systems, whereby the rear wheel tends to produce a toe-out movement. In order to produce a toe-in movement in the rear wheel under the application of a rearward force, the magnitude of the toe-in must be larger than that of the toe-out. However, where the deformation characteristics of the lateral link systems are set to be non-linear so as to control the toe direction relative the lateral force, the change in the toe-in movement in the rear wheel, which is caused by deformation in the lateral link systems, also exhibits non-linear characteristics. No consideration has been taken of this point, namely, the change in the toe movement in the rear wheel produced by the rearward force acting on the rear wheel. Hence, there remains a possibility that, when a rearward force of a certain magnitude acts on the rear wheel, the change in the toe-out direction of the rear wheel caused by the deformation in the lateral link systems can become larger than that in the toe-in direction thereof caused by the rearward traveling of the wheel support, by which the rear wheel can be undesirably changed in its attitude in the toe-out direction.